#2...unfortunately you can not set that scale in a imported sketch I know of. Just a couple of days ago I kept wondering why my dimensions on my I-Beam wear wrong. Yup, the scale was just a little off and I didn't catch it initially. It's really sad that it doesn't simply defualt to 1 and then allow you to change it if necessary.
#3...You can set the snap point on the imported geometry by left mouse clicking on vertex's or points. The snap point will align or be concident to references but won't automatically add the constraints so that is why it adds the weak dimension to fully constrain the model. Another silly thing that is almost does right.